Phased antenna array



Dec. 16, 1952 R. G. cLAPP ETAL PHASE@ ANTENNA ARRAY Filed Aug. 25, 1950 Patented Dec. 16, 1952 PHASED ANTENNA ARRAY Richard G. Clapp, Haverford, and Samuel H. Colodny and Bernard Wise, Philadelphia, Pa., assignors to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application August 23, 1950, Serial No. 180,925

7 Claims.

The invention herein described and claimed relates to antenna arrays.

While not limited thereto, the present invention may be used to particular advantage in a broadside or other type of phased array. In such arrays, the phase of the current in all of the radiators is substantially the same. If the currents in all radiator elements have the same amplitude as well as the same phase, the array is commonly said to have uniform illumination, whereas if the currents in the various radiator elements are in phase but the current amplitudes decrease (or increase) uniformly from the central section out to the end sections, the array is frequently said to have a tapered illumination. While not limited thereto, the present invention may be used to particular advantage in an array having tapered illumination.

A broad object of the present invention is to provide simple means for controlling the amount of radiation from a half-wave radiator.

Another object is to provide simple means for controlling the radiation pattern of a phased array.

A more specific object is to provide an array of simple construction having a tapered illumination.

A still more specific object is to provide a binominal array of simple construction.

The foregoing objects are achieved, in accordance with the present invention, by providing a fold or reentrant portion of proper length in the maximum-current region of the radiator element. The conductors forming the sides of the fold are closed spaced, as for example, one hundredth of a Wavelength apart. The currents in each side of the fold now in opposite directions, cancellation of fields occurs, and there is, consequently, no radiation from the high-current region in a radiator having such a folded portion. By properly choosing the length of the fold or reentrant portion, in the various radiator elements of a phased array, as for example, by making the reentrant portions progressively larger by proper amounts from the central radiator section out to the end sections, the radiation from each element of the array may be readily and properly proportioned to achieve the desired binomial or other tapered distribution of eld strength. Negligible disruption of phase distribution or of continuity in antenna-element construction results since the total conductor length of each radiator element of the array, inclusive of the reentrant portion, remains vvery close to one-hall wavelength.

The invention will be better understood from a consideration of the following detailed description taken together with the accompanying single gure of drawing wherein is illustrated a broadside array having the present invention incorporated therein.

Referring now to the drawing, ten half-wave radiator elements Il to 29 are shown arranged in a broadside array, five sections long and two elements high. The radiator elements are so spaced vertically that the transposition pieces 2l 'to 28, which connect the elements of the adjacent sections, are each one-half wavelength long, or at least an integral odd number of half-wave lengths long, so that the currents in the various half-wave radiator elements may be in phase. The central section of the array, comprising dipoles I5 and I6, is fed by transmission lines 29, 30. Each radiator element, other than those of the central section, contains a fold or reentrant portion .3l-38. It is to be particularly noted that the folds are located in the maximum-current region of the radiator elements. As previously indicated, there is no radiation from the folds since the conductors forming the sides of the folds are closely spaced, the currents in each side of the fold are in opposite directions, and cancellation of fields occurs.

To achieve binomial distribution of field strength, the folds in the end-section elements are made reentrant to a greater extent, and by a proper amount, than the folds of the intermediate-section elements. The conductor length of each radiator element, including the conductor length of the fold or reentrant portion, is maintained at, or close to, one-half wavelength, measured in or on the condu-ctor. The radiating portions of the end-section elements are, therefore, shorter in length than the radiating portions of the intermediate-section elements, which in turn are shorter than those of the central-section elements. Consequently, due to the folds, the field strength contributed to the main beam by the intermediate-section elements is substantially less than that from the central-section elements; and the field strength contributed to the main beam by the end-section elements is substantially less than that contributed by the intermediate-section elements.

It will be clearly evident, then, that by the simple device of merely placing folds of proper lengths in the region of maximum current in the various half-wave radiators, the contribution of the various radiator elements to the field strength of the array, measured at a distance, can be made to conform to the coeflicients of a binomial expansion, or for that matter, to any other desired proportion.

The advantages of a so-called binomial array are well known. In short, it is well known that a binomial array has substantially reduced minor lobes, as compared with a uniformly-illuminated array. An array is said to be binomial when the currents in the various radiator elements are in phase and of such proportional amplitudes that the relative field strengths .contributed to the main beam by the various radiator elements correspond Yto the coefficients of the expansion (a-i-b) "-1 where 1L is the number of sections in the array. For example, the array shown in the drawing has five radiator sections. Hence, n equals 5 and (n-l) equals 4. The coefficients of (a-i-b)4 are 1, 4, 6, 4, l. Hence, to achieve a binomial distribution, the folds in the two end sections should be made of such length that the field strength contributed to the main beam by each end section, measured at a distance from the radiators', is equal approximately to one-sixth of that contributed by the central section. And the folds in the intermediate sections should be made of such length that the field strength contributed to the main beam by each intermediate section approximates four-sixths of that contributediby the central section. The dimensions and physical arrangement, including the physical supports', of the transposition pieces 2|28 have an appreciable effect upon the amount of power passing from one radiator section to an adjacent section, andas a consequence, for a binomial distribution in an array employing transposition pieces, the optimum dimensions ofthe folded portions will be dependent, among other things, upon ,the design of the transposition pieces and supporting structure therefor. Perhaps mention should be made of the fact that, since the transposition pieces should be maintained at a length of one-half wavelength, if the spacing s' between radiator elements is maintained equal for all radiatorv sections, the distance d between radiator centers will necessarily decrease as the size of the folds increases and the length of the radiating portions of the radiator elements decreases. This is a satisfactory design. if desired, the distance d maybe held xed, in` which'case the spacing s will necessarily decrease as the size of the folds increases and the length of the radiating portions decreases.

It will'now be readily understood: that, in accordance with the inventive concept of the presentf-invention, a fold of suitable size is placed at the current antinode in a half-wavel radiator to reduce the radiation field strength by the desired amount. Thus, the field strength contributed to the main beam by each element in the array may be readily controlled, and, if desired, may be so controlled that the contributions of the various radiator elements are proportional tothe coeiiicient of a binomial expansion. This is indicated graphically in the drawing by the dotted lines.

If 4the array be a broadside array comprised of a substantial number of radiator elements in the vertical as well as: in the horizontal plane, binomial contribution to the radiation field may, of course, be eiiected vertically as well as horizontally by properly proportioning the folds vertically as well as horizontally throughout the array.

In the foregoing description, and also'A in some of the appended claims, reference is made to the held strength contributed toy thev main beam by the various radiator elements. It will be under- 4 stood that the eld strength referred to is that measured at a distance from the radiator elcments.

It will also be understood that where, in the description and in the claims, it is stated that the radiator elements (or transposition pieces) have a length substantially `equal to one-half wavelength, the one-half wavelength referred to is in the radiator element (or transposition piece) itself, as distinguished from one-half wavelength in free space.

Having described our invention, we claim:

1. A' broadside antenna array comprising at least fiv'e radiator sections arranged in a substantially straight line, each of said sections being comprised of a plurality of substantially parallel radiator elements arranged in a common plane; transposition conductors connecting the radiator elementsv of adjacent sections, said transposition conductors being one-half wavelength long at the operating frequency; and "a" transmission line connected to a central section of. the array;' said array being characterized by the fact that each of said radiator elements is comprised of a' conductor having a conductor length equal substantially to one-half wavelength at the-operating' frequency, said radiator elements of the e'ndl sec tions and of the sections intermediate' end and central sections' each having! a' foldedA nonradiating portion at the mid-point of saidradi-` ator elements. y Y l 2. A broadside antenna array asl claimed in claim l characterized by the fact thatthe said folded non-radiating portions in the intermediatesection'V elements are shorter than those in the end-section elements by Vsuch amounts that the relative field, strengthsv contributed to the main beam by the end, intermediate, central, inter'- mediate and end sections .correspond respectively to the coeicients of the expansion (a-l-b) 1H, where n equals the number of sections' ini the array. 1

3. A phased antenna array comprising: at least ve sections arranged substantially in line, each of said-sections being comprised .of a plurality of antenna elements arranged ina common' plane and connected together by antenna-current phasing means, each of said antenna elementsv comprismg a conductor having a conductor length'sub'- stantially equal to one-half' wavelength art the operating frequency, the central section'elem'ents being open at the element mid-point tor provide terminals for said'arra-y, elements of the endsectionsy and of the` sectionsV intermediate.. the vend and' central'sections each having a re-entrant portion at the element mid-point, the re-entrant portions being' progressively smaller looking from the end-section'- elements towardlthe central-.f-

sect'ion terminals. 4*. A phased antenna array as claimed in claim 3` furtherv characterized. by the fact 'that said re-i entrant portions are sozproportione'd ini size'that the relativeeifectiveness of the endinterm"ediate, central, intermediate, and end-section elements as contributing elements to the array correspond respectively tov the coeicients ,of the' expansion (a+-bind, where nequalsvthe number of 'sections in tl'iefar-ray.r l' 5. An' antenna array comprising aplurality of antenna elements connected together, said elements comprisingconductors placedsubstantially inline-ina common. plane, eachof said elements having a conductor length equalsubstantially to one-half wavelength at the operating frequency, at least one of said elements beingopen at its mid-point to provide a pair of terminals for said array, at leastV some of said elements having a re-entrant portion at the element mid-point, the re-entrant portions being of progressively different size looking from an end-position element toward said antenna-array terminals.

6. An antenna array comprising a plurality of antenna elements connected together, said elements comprising conductors placed substantially in line in a common plane, each of said elements having a conductor length equal substantially to one-half wavelength at the operating frequency, at least one of said elements being open at its mid-point to provide a pair of terminals, at least some of said elements having a folded portion at the element mid-point, said folded portions being of different size.

7. An antenna array comprising a plurality of antenna, elements connected together, said elements comprising conductors placed substantially in line in a common plane, at least some of said elements having a re-entrant portion at the mid- REFERENCES CITED .i The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,813,143 Bruce n July 7, 1931 1,874,983 Hansell Aug. 30, 1932 Franklin May 9, 1933 

